Guys, Why does he keep lifting his top in front of me to annoy me?

Hello,

Right I need some advice on what to do! So there is a guy (not dating or ever spoken to) we usually give evils to each other if we make eye contact. Anyhoo the issue here is we go to the same gym and for some reason he is always behind me! So if I’m on a certain machine I can see him behind me in the mirrors! He also keeps lifting his top to flash his stomach and continuously do this as he can see this annoys (he can see my reactions) there are other machines but he’s always behind mines. He has tried to come near me before but I’ve felt uncomfortable and moved away! There other day I was looking at another guy and he started looking at him too which was so awkward. My question is what is his problem with me?
Guys, Why does he keep lifting his top in front of me to annoy me?
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